Lecture 3: Identity Theory

Identity theory is a kind of materialism developed as a reaction to work in psychology and the physical sciences in the mid 20th century. It essentially boils down to these statements:

1) Minds are identical to brains
2) Mental states are identical to brain states
3) The realm of the mental is a subset of the realm of the physical

Proponents of this theory state that this claim is a contingent fact about the nature of the mind and the brain; it makes no attempt to explain the meaning of mental terms and so isn't a semantic thesis like logical behaviourism (e.g. 'pain' means physiological state X).

One identity theorist, Smart, claimed that it ought to be a strict identity statement. By this he meant that mind and brain refer to exactly the same thing, i.e. if minds are identical to brains, then brains are identical to minds. Strict identity statements are therefore logically symmetrical. An "un-strict" identity statement would be assymmetrical, for example: rain is identical to bad weather, but bad weather could be rain, sleet, snow, etc.

Identity theory is deemed to be contingent because of the history of the theory. Generally, necessary facts are deemed to be a priori, and so discoverable through study of language, e.g. "one plus one equals two", or "a bachelor is an unmarried man". But because identity theory came from scientific discoveries, the thought is that it cannot be necessary. But then if two things are identical, must that fact not be necessary? One cannot say that in conscious beings on earth, their brains are identical to their minds, but that it is possible that that wouldn't be the case, since that contradicts the theory.
One can however point out that the strength of gravity at the earth's surface is a necessary fact, and yet we only discovered that after thousands of years of scientific investigation. Necessary facts needn't be a priori facts accessible through analysis of language.